EFFECTS OF COLD EXPOSURE ON BLOOD FLOW TO THE MAMMARY GLAND AND TISSUES OF THE HIND LIMB OF THE LACTATING EWE

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Abstract
Mammary blood flow was measured in cold-exposed lactating ewes using an electromagnetic blood flow probe on the mammary artery to monitor acute responses, and by injecting radionuclide-labelled microspheres to assess chronic effects. During a period of acute cold exposure (−5 to −15 °C; 4 h) mammary artery blood flow and udder surface temperature decreased markedly when the animal was standing; heart rate increased but rectal temperature remained relatively unchanged. Lying down insulated the mammary gland resulting in increased mammary artery blood flow and udder surface temperature. After a period of prolonged cold exposure (0 °C, 8 wk), udder size and mammary blood flow tended to be lower in comparison to values obtained from ewes housed at 21 °C. Mammary blood flow/100 g tissue was reduced for udder skin (P < 0.07) and teat (P < 0.03) but tended to be higher (P > 0.10) for connective tissue as a result of cold exposure. Calculated mammary blood flow:milk yield ratios were 664 ± 179 for control and 360 ± 110 for cold-exposed ewes. Blood flow was increased to the popliteal fat depot (P < 0.01) and tended to be higher to the gastrocnemius and semimembranosus muscles (P > 0.05) but was decreased to the skin of the thigh (P < 0.05) and lower leg (P < 0.10) as a result of cold exposure. The present results indicate that tissue blood flow redistribution in the lactating ewe during cold exposure is similar to that in nonlactating ruminants and that moderate reductions in mammary blood flow during cold exposure can occur without detrimentally affecting milk secretion in the lactating ewe. Key words: Cold, ewes, mammary blood flow, hind limb blood flow
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